Why is clear epoxy not often used to fill cracks in live edge slabs?

Question

I've worked with a few live edge slabs in the past, but the one I have now is the first one with a sizable crack. I don't like the look of butterfly keys, and I don't believe that this crack needs much reinforcement, but I was going to fill it with West epoxy just in case (and as a way to finally try using it).

The thing that has surprised me in the videos I've seen is that all of them use a very dark tint, many going with straight black. It creates a very striking aesthetic effect, but I don't think I want to pull the visual focus away from the wood like that. I was considering using the epoxy without a tint so that the reinforcement is relatively invisible, and went with the 207 hardener for this purpose.

However, I have not been able to find a single example of clear epoxy being used. I've done some googling but in addition to not seeing any examples, I also cannot find any discussion of why tinting is so common. Since it is done so rarely I assume there must be a reason, and don't want to ruin my slab due to my inexperience, so:

Why is clear epoxy not used? What considerations should go into a decision about whether, and how, to tint?

Answer 1

Why is clear epoxy not used?

Two related reasons I can think of plus a third unrelated. The first is just because people don't want to make their fills transparent (or to put it another way, they really like coloured fills), at a guess this would account for most of it. The related reason is that maybe some users know getting the fill completely bubble-free can be tricky* so they're afraid to try.

Third is that some users will have enough knowledge of epoxy to know it discolours (badly) with UV exposure, so a clear epoxy fill will eventually look just plain awful.

If you want to fill with a clear resin then look into one of the clear casting resins that markets itself as having good UV resistance. These will be invariably a polyurethane I think. But two points to note, 1) these can be very moisture-sensitive, so you may have to ensure your wood is particularly well dried or apply a barrier of some sort before the fill is poured, and 2) a warning: some sticker shock may ensue.

in the videos I've seen is that all of them use a very dark tint, many going with straight black. It creates a very striking aesthetic effect, but I don't think I want to pull the visual focus away from the wood like that.

Well you can colour a resin fill any colour you like, literally any colour. From a tinted clear or 'candy' effect to solid colours to filled with powdered wood, metal or minerals, the choice is endless.

If you fill the resin with fine sanding dust from the wood you're using the colouring will be similar but darker, somewhat like end grain after the finish goes on, which can tone in fairly well since it's not that dark. But if you'd like it closer in shade you need to either lighten the mixture somehow (add in a little white/cream/ivory paint or partially fill using a light-coloured/white filler material) or, mix it using the dust from a different piece of wood, possibly from a different species entirely.

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*Obviously if you have bubbles trapped in a typical solid-colour fill (and there usually are) you can't see them, although some can be exposed when the fill is being made flush with the surrounding surface.

Answer 2

I've used clear epoxy and tinted, it just depends on the project. Clear is generally harder to get right. If you have contaminants they will show or cloud the final product. For me, tinting is either with black or very dark brown, no matter the wood color. I do that so that it does not look like I was trying to match the wood, which would be really tough with epoxy. Plus, if the piece of wood you're working with is pretty enough it really wont pull you away from it.

I would disagree with aaron in that the choice is entirely aesthetic, cost plays a role too. I recently did a piece of live edge cedar for a window sill that had several knots that needed filled. I used West Systems 404 & 206 and since the knots were large I decided to add in some West Systems High-Density Filler (40415) to add some more bulk to the filling. This helps with run-out, even though the backside was taped well, and I can get away with using less epoxy (expensive stuff). In this application I went clear and learned a valuable lesson. If you choose to use filler, always tint or by happy with a white/cloudy appearance. I've not coated these spots yet with anything but I don't expect them to 'clear up' once I do.

Answer 3

The choice is entirely aesthetic. I have only ever used clear epoxy to fill cracks because i think that looks best. Sometimes a striking effect is achieved with other fillers too, eg. turquoise.

Answer 4

I faced a similar conundrum recently - I wanted a clear epoxy finish to preserve the natural appearance of the wood. In the process of making my piece I made various mistakes with the epoxy, including using a non UV resistant one, and allowing some bubbles to set in the piece (which is very difficult to avoid entirely).

You can check out my project (which I did as a novice) if you like. After doing it it makes more sense to me why people use a tint so often:

• UV induced yellowing is not visible
• bubbles are not visible
• transparent epoxy looks pretty dark anyway unless there is light shining through it